1. Field
This disclosure relates to a vehicle maneuvering system and method for intercepting and destroying ballistic missile re-entry vehicles and other targets.
2. Description of the Related Art
Systems for intercepting ballistic missile threats typically reply on a kinetic kill vehicle (KKV), also termed a “hit-to-kill” vehicle, to destroy the threat re-entry vehicle by way of physical collision. A missile carrying the KKV, or a plurality of KKVs, is launched to the place the KKV in a position proximate the trajectory of the target re-entry vehicle. The KKV then detects and tracks the target vehicle and navigates to attempt to physically collide with the target. Exemplary KKV development programs include the Exoatmospheric Kill Vehicle (EKV), the Lightweight Exoatmospheric Projectile (LEAP), and the Multiple Kill Vehicle (MKV).
KKVs are designed to intercept and destroy the target re-entry vehicle during the mid-course phase of the re-entry vehicle flight. The interception may occur above the earth's atmosphere at altitudes in excess of 100 miles. The combined speed of the KKV and the target re-entry vehicle may approach 15,000 miles per hour, or over 20,000 feet per second, such that a collision between the KKV and the re-entry vehicle will severely damage or destroy the re-entry vehicle. The KKV typically attempts to maneuver to assume a trajectory that is a reciprocal of the trajectory of the target re-entry vehicle, which is to say that the kill vehicle and target re-entry vehicles are traveling on the same or nearly the same trajectory in opposing directions. In reality, the kill vehicle will deviate from the desired reciprocal trajectory by an error amount, commonly termed the CEP or circular error probable. The CEP is defined as the radius of a circle about the desired trajectory that would contain the kill vehicle 50% of the time. A normal distribution of the vehicle navigation errors is commonly assumed, such that the kill vehicle will be within a circle having a radius of twice the CEP 93% of the time and within a circle having a radius of three times the CEP more than 99% of the time. Given the relatively small sizes of the hit-to-kill vehicle and the target re-entry vehicle and the extreme closing speed, the CEP of the KKV may need to be less than a fraction of a meter to provide a high probability of colliding with the target re-entry vehicle.
To meet these extremely precise navigational requirements, the KKV may include an on-board sensor and tracking system to track the target up to the point of collision. The KKV typically includes a divert and attitude control system (DACS) which is used to maneuver the KKV to the trajectory required to intercept the target. The DACS has a plurality of attitude thrusters that may be used to control the attitude or orientation of the KKV about three axes of rotation. The attitude thruster may be used, for example, to keep the target within the field of view of the on-board sensor. The DACS may also include a divert subsystem used to change the trajectory of the KKV in response to the target tracking system. A typical divert subsystem may include four nozzles disposed at 90-degree intervals about a perimeter of the KKV. Each nozzle may be used to exhaust gas in a direction generally normal to a longitudinal axis of the KKV which is typically aligned with the direction of travel. Gas may be exhausted selectively through the four nozzles to accelerate the KKV in a desired direction generally normal to the direction of travel to maneuver the KKV to intercept the target.
In typical divert subsystems, the gas exhausted through the nozzles of the divert subsystem may be provided by an independent liquid fuel rocket motor coupled to each nozzle or by a common gas supply such as a gas reservoir or a rocket motor. When independent rocket motors are used, the direction and magnitude of the thrust produced may be controlled by metering the fuel supplied to the rocket motors. When a common gas supply is used, the direction and magnitude of the thrust produced may be controlled by metering the gas supplied to the respective nozzles. When the common gas supply is a rocket motor, the combustion gases may be metered through so-called hot gas valves. The piping, valves, actuators and other components required to meter either liquid fuel or exhaust gas to multiple divert nozzles increases the cost and complexity of the KKV.
Throughout this description, elements appearing in figures are assigned three-digit reference designators, where the most significant digit is the figure number and the two least significant digits are specific to the element. An element that is not described in conjunction with a figure may be presumed to have the same characteristics and function as a previously-described element having a reference designator with the same least significant digits.